In general, a turbocharger used for supercharging of an internal combustion engine is provided with a waste gate valve at a turbine part which is configured so as to bypass a part of exhaust flow without passing through a turbine wheel, for supercharging pressure control. In a patent document 1, as a driving mechanism for the open/close driving of the waste gate valve, a so-called swing type mechanism is disclosed in which the linear motion of a rod of an electric actuator is converted to the rotational motion of a rotation shaft through a link and then a poppet type valve body which is supported on the distal end of an arm fixed to the rotation shaft oscillates.
In such the above waste gate valve, as described in the patent document 1, in a part of the driving mechanism, a small clearance exists, for example, between the distal end of the arm and the poppet type valve body or between the distal end of the rod and the link.
On the other hand, at the time of the idling in a state in which the internal combustion engine is cold, although an ignition timing retard is executed for catalyst warm-up of an exhaust system, the pressure fluctuation of exhaust gas, specifically, exhaust pulsation becomes large with the ignition timing retard. In addition, in general, at the time of idling, the opening degree of the waste gate valve is controlled to full opening to reduce exhaust resistance, and a part of the exhaust flow passes through the periphery of the valve body.
Therefore, at the time of the idling in the engine cold state, in which the exhaust pulsation becomes large, the valve body is vibrated caused by the above clearance, and consequently, abnormal sound tends to occur.